CHARLESTON, S.C. — Once upon a time, Mark Sanford might have been a contender, but there’s too much water under the bridges that stretch from this city of steeples to his erstwhile home on Sullivan’s Island.

The disgraced former South Carolina governor and congressman announced Sunday that he’s running against Donald Trump for the 2020 Republican nomination. The third challenger to toss his hat into the wishing well of magical thinking, Sanford says he plans to talk about the skyrocketing debt, tariffs, trade and tone. Perfect. That’ll ignite the crowds and knock the grand poobah of pomp and propaganda off his game.

You can just see it: The boyish Sanford — an itinerant stranger in his own strange land — going toe to toe with the swamp-menacing Trump. It would be worth the price of a ticket. Trump’s other two GOP opponents, former Massachusetts Gov. Bill Weld and former Illinois Rep. Joe Walsh, may as well grab one while they last.

Nevertheless, the buzz does what buzz does. In the days following Sanford’s announcement and a series of cable-TV appearances, you’d have thought the former governor were the deus ex machina of the GOP. Recent commentary from conservatives has been dripping with so much honey you don’t know whether to build a hive or kill the drones.

The narrative-shmarrative is that Sanford is an old-school Republican whose concerns are focused on a strong, bootstrap economy and, well, that’s about it so far. Also, BIG HEADLINE, he believes in climate change and legal immigration because, what life form other than Trump’s most fervent supporters doesn’t?

Further to Sanford’s coronation as GOP savior, according to Republican strategist Liz Mair writing Monday in The New York Times, he’s a bigger threat to Trump than his co-challengers because he was never a “Never Trumper.” Unlike Walsh and Weld — a strong law firm name if things go awry, as surely they will — Sanford appears to be uninterested in making the race all about Trump, even though Trump’s anti-endorsement in 2018 led to Sanford’s congressional primary defeat.

Plus, wrote Mair, Sanford is more “nuanced.” Perhaps she was thinking of the subtle differences between Argentina and the Appalachian Trail, where in 2009 the then-governor Sanford told everyone through a spokesperson that he’d be hiking for a few days but instead found himself in South America with his mistress?

Mair insists that the tryst that ended Sanford’s governorship, as well as his marriage, was “the least-scandalous scandal in modern political history” because, after all, he only had an “extramarital affair because he fell in love and got engaged to the woman.”

This confection would be news to South Carolinians who were appalled by his deceit and repulsed by his weepy news conference to confess his sins. Such a cavalier dismissal of a family betrayal would also be news to ex-wife Jenny Sanford, who wrote a book, “Staying True” about it. While you’re browsing, by all means pick up “The Speechwriter,” by Barton Swaim, Sanford’s speechwriter for the latter part of his administration. It’s hilariously funny and a poignant memoir of a tenure of absurdity.

It is absolutely true that Sanford, 59, is a time-tested conservative on budgetary matters, as my Washington Post colleague Jennifer Rubin argued under the banner headline “Mark Sanford might be the Republicans’ last chance.” No one can accuse him of being a fake conservative, she wrote.

Indeed, not. As governor, Sanford was such a budget cruncher that he brought two baby pigs, one under each arm, to the statehouse to make his point about — get it? — pork.

It is quite possible that most or many Americans don’t care what Sanford did in his personal life, but the nicknamed “Luv Guv’s” philandering meanderings were public matters by virtue of two facts: The highest-ranking official of the state lied about his whereabouts and was unreachable. He simply slipped the reins of government and followed his passion, which was concerned with “issues” having nothing to do with matters of state.

It’s not the economy, it’s character. Only someone as despicable as Donald Trump could make a man like Mark Sanford palatable. Sanford’s well-reasoned concerns about the unfathomable debt, his low-key, soft-spoken style and his cool Southern manner might have made him a terrific presidential candidate in another time, especially alongside his tough, accomplished wife and central-casting sons. But that time has passed.